Zhu Lixia

Crystal structure and characterization of Rb2Ca[B4O5(OH)4]2·8H2O

Abstract Dirubidium calcium tetraborate octahydrate, Rb 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O, was prepared by reaction of Rb-borate aqueous solution with CaCl 2 and its structure has been determined by single-crystal X-ray diffraction data. It crystallizes in the orthorhombic system, space group P 2 1 2 1 2 1 with unit cell parameters, a=11.536(2) A , b=12.639(2) A , c=16.690(4) A ; Z =4, V=2433.5(8) A 3 . The structure contains alternate layers of [B 4 O 5 (OH) 4 ] 2− polyanions separated by water molecules and Rb, Ca cations. The isolated [B 4 O 5 (OH) 4 ] 2− is constructed from two BO 3 (OH) tetrahedron groups and two BO 2 (OH) triangular groups joined at common oxygen atoms. The two BO 3 (OH) tetrahedron groups are further linked by means of an oxygen bridge across the ring. The Ca 2+ ion displays seven coordination, while the two non-equivalent Rb + ions display nine and seven coordination, respectively. Infrared and Raman (4000–400 cm −1 ) spectra of Rb 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O were recorded at room temperature and analyzed. Fundamental vibrational modes were identified and band assignments were made. The dehydration of this hydrated mixed borate occurs in one step and leads to an amorphous phase which undergoes a crystallization.

Crystal structure and thermal behavior of Rb2Co[B6O7(OH)6]2·4H2O

Abstract A crystal of the complex borate Rb 2 Co[B 6 O 7 (OH) 6 ] 2 ·4H 2 O was synthesized in the molar ratio Rb 2 O/CoCl 2 /B 2 O 3 =4:1:9, and its structure was determined by single-crystal X-ray diffraction. It belongs to the P 1 triclinic space group, with the following unit cell parameters: a =7.549(1) A, b =7.872(1) A, c =10.980(2) A, α =107.87(1)°, β =94.83(1)°, γ =90.27(1)°, Z =2, V =618.45(19) A 3 . The crystal structure was solved from 2162 independent reflections until R =0.0127. The crystal structure of Rb 2 Co[B 6 O 7 (OH) 6 ] 2 ·4H 2 O consists of [B 6 O 7 (OH) 6 ] 2− polyborate anions, Co–O octahedra and Rb–O polyhedra. The isolated [B 6 O 7 (OH) 6 ] 2− polyborate anions are separated by free water molecules and Rb and Co cations. Dehydration of this hydrated mixed borate occurs in two steps and leads to an amorphous phase which undergoes crystallization.